1. Field of the Invention
This invention pertains to certain novel esters of pentavalent phosphorus acid and to plastic compositions containing these esters as flame retardants therefor.
2. Description of the Prior Art
During the past several years, a large number of flame retardants have been developed for use with an almost equally large number of flammable materials. Cellulosic materials such as paper and wood and polymeric materials such as polyolefins, polyesters, polyurethane and polystyrene are just two examples of materials for which flame retardants have been developed. For any class of flammable materials, such as synthetic type polymers, those skilled in the art have long been aware that some flame retardant additives are more effective in polymers and polymeric compositions than other flame retardant additives. This is because the efficacy of any flame retardant in polymers or polymeric compositions is measured not only by the flame retardant capability of the additive but also by the ability of the additive to improve or modify, or at least not to detract from, other physical or mechanical properties of the polymer or polymeric composition. The mere fact, therefore, that most flame retardants contain halogen and phosphorus atoms does not assure that any given halogenated or phosphorus-containing compound will impart usable flame retarding characteristics to all or even to any polymeric system. Furthermore, as those skilled in the art have improved the flame retardancy of many polymeric materials, they have been simultaneously required to provide the necessary flame retardancy with a minimal effect upon other properties of the polymer such as the light stability, processability, and flexural, tensile and impact strengths. Also, it has been the desire of those involved in the art of flame retardants to provide flame retardants having a durable lasting effect. Balancing all of the foregoing considerations and thereby developing polymeric compositions with good flame retardant characteristics as well as a satisfactory balance of other properties is, consequently, a task which has in the past and presently continues to require the exercise of a high degree of inventive skill.
The prior art considered in the preparation of the instant application includes U.S. Pat. Nos. 3,132,169 to Birum et al., 3,324,205 to Carpenter et al., 3,385,801 to Birum et al., 3,391,226 to Birum et al., 3,433,856 to Friedman, 3,471,592 to Friedman, 3,781,388 to Jenkner et al., 3,830,886 to Davis et al., and German Pat. No. 2,416,663 to Burke.
In particular, U.S. Pat. No. 3,132,169 to Birum et al. discloses flame retardant esters of pentavalent phosphorus acids, which esters contain both chlorine and bromine, and which are selected from the class consisting of a phosphate of the general formula ##STR2## wherein R is selected from the class consisting of hydrogen, alkyl and haloalkyl radicals of from 1 to 2 carbon atoms, R' is selected from the class consisting of hydrogen, alkyl and haloalkyl radicals of from 1 to 5 carbon atoms, R" is selected from the class consisting of R' and hydrocarbyloxymethyl radicals of from 1 to 8 carbon atoms, wherein one R" at a pair of adjacent carbon atoms must be hydrogen, and n is an integer from 0 to 1.
U.S. Pat. No. 3,781,388 to Jenkner et al. discloses flame-proofing agents having the general formula ##STR3## wherein R.sub.1 is a halogen-containing alkyl radical containing 2 to 4 carbon atoms and 1 to 3 halogen atoms; R.sub.2 is an alkyl radical containing 2 to 4 carbon atoms which may also optionally contain at least one halogen atom and/or at least one OH group; and R.sub.3 is an alkyl group containing 2 to 4 carbon atoms and one OH group.
U.S. Pat. No. 3,830,886 to Davis et al. discloses flame retardant additives of the general formula ##STR4## wherein n is zero or one; R is a lower alkyl, phenyl or alkylated phenyl having one to three lower alkyl substituents, R' is R or ##STR5## and at least one R" is Br or Cl and each remaining R" is OH, Br, or Cl.
Birum et al. does not disclose that the compounds therein can contain hydroxyl substituents attached to the neopentyl group. As those skilled in the art of flame retardants know, the indiscriminate substitution of a hydroxyl group for a halogen or hydrogen atom of a compound will often result in a dramatic decrease in the modified hydroxy substituted compound's hydrolytic and thermal stability. However, by the use of a high degree of inventive skill, it was possible to effectuate a substitution of a hydroxyl group for a halogen or hydrogen atom and still maintain the basic physical properties of the nonhydroxyl-containing compound. The net result of this inventive skill is that one now can produce a reactive flame retardant capable of reactively being bound into a polymer chain, e.g., polyurethane and polyester, and thereby reducing the migration of the flame retardant and the subsequent flame retardancy loss of the polymeric composition. This result has long been sought after and much desired in the art of flame retardants.
Davis et al. discloses triesters of phosphorus acid in which one of the ester groups is a lower alkyl group. Davis et al. state that "prior art fire-retardants suffer from a number of disadvantages such as their tendency to produce hydrogen halides such as HBr when heated" and that the "new compounds (of their invention) have unusual resistance to thermal and hydrolytic decomposition and are therefore superior fire-retardant additives for wood, textiles, plastics, and the like." Davis et al, appear to have acheived this unusual hydrolytic stability by using groups having no hydrogen containing carbon atoms in a beta position relative to halogen bearing carbon atoms.
Applicant has found, contrary to the teachings of the prior art, that the instant compounds possess unusual hydrolytic stability despite the fact that they may possess halogen atoms adjacent to the beta carbon atoms.
Jenkner et al. disclose phosphates containing two haloalkyl groups of from 2 to 4 carbon atoms and a single hydroxyalkyl group of from 2 to 4 carbon atoms. These phosphates, however, are thermally and hydrolytically less stable, and therefore less useful than applicant's instant compounds.